Difference Between Azithromycin and Erythromycin

Both Azithromycin and Erythromycin are macrolides that are used to fight a variety of infections, especially those of the soft tissues, upper and lower respiratory tract and uro genital infections. Azithromycin is a derivative of Erythromycin. However, they differ in their mechanism and onset of action. There are a number of factors which may determine the choice of medication the doctor prescribes for you.

Azithromycin is usually administered in the form of an oral suspension or as a tablet. The main convenience of the tablet form is that it can be taken as a single pill once daily. Depending on the severity of your symptoms and your exact cause of infection, a doctor may prescribe a dose of either 250 mg or 500 mg. Your doctor may also prescribe a double dose on the first day of treatment and then follow it up with four or five days of treatment.

Erythromycin is basically used for infections where people are resistant to penicillin. It provides a wider coverage for upper respiratory tract infections. Erythromycin might be prescribed by your doctor in the form of tablets, slow release capsules, ophthalmic solutions and ointments, gels etc. The exact mechanism by which Erythromycin acts is not known. However, it is known that it may have some sort of bactericidal action. Azithromycin functions by stopping the growth of the bacteria inside the body. This is done by obstructing their protein synthesis.

Both Azithromycin and Erythromycin may have a number of adverse effects including nausea, diarrhea, vomiting and abdominal pain. For this reason, your doctor may not prefer them, especially Erythromycin, as a first line drug. Patients may also have allergic reactions to these medications, including urticaria and anaphylaxis. Azithromycin has also been increasingly used as a drug of choice for treating infants. It is also used very frequently for people whose immunities are compromised for some reason.

Azithromycin displays a prolonged terminal half life. Reasons for this may be the relatively extensive uptake and release of the drug from the tissues. Erythromycin is basically metabolized in the human liver. It is mainly eliminated in the bile and some of it is also disposed off in the urine. Erythromycin’s elimination half-life is about 1.5 hours. Both these antibiotics may interfere with the functioning of birth control pills. So, if you are taking these, you should always inform your doctor before starting off on the medications.

Both Azithromycin and Erythromycin are prescribed by doctors for treatment of infections. However, your doctor may prefer administration of Azithromycin if you are pregnant. Azithromycin is easier to administer (in the form of a single pill per day) and your doctor may prefer it for this reason. Some patients also report that they have fewer reactions with Azithromycin than they do with Erythromycin.

However, you may find that Azithromycin is costlier compared to Erythromycin. You doctor will be able to guide you on the best option. He will evaluate your infection and prescribe the medication that is most suitable for you.

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Written by : Purpa Mukherjee.
and updated on September 18, 2009

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